ACVR2 is a member of the transforming growth factor beta (TGF-β) receptor family. It is a 70-75kDa protein consisting of 513 amino acids. It is a transmembrane receptor for activin, with a cysteine-rich extracellular ligand-binding domain, a single pass transmembrane domain, and an intracellular domain with constitutive serine/threonine kinase activity. Upon binding activin, ACVR2 associates with and phosphorylates ACVR1. ACVR1, in turn, phosphorylates Smad2 and/or Smad3. Phosphorylated Smad2 and Smad3 associate with Smad4, translocate to the nucleus, and regulate gene expression. There may be other non-Smad pathways in activin signal transduction. These include the RhoA-ROCK-MEKK1-JNK and MEKK1-p38 pathways. In addition to activin, other ligands such as myostatin, nodal, and bone morphogenetic protein 7 (BMP-7) may also bind to ACVR2 and affect signal transduction.